Biomedical subjects

Fuchuan Sun

Publications and source records attributed to Fuchuan Sun.

10 recordsLinked to original sources

PubMed2005

Properties of pupillary responses to dynamic random-dot stereograms.

Pupillary response can be elicited by a number of visual stimuli. In the present experiments, the pupillary responses to stereo gratings with various spatial frequencies and disparity amplitudes were measured. The spatial frequency was from 0.1 to 1.2 cycles per degree (cpd), and the disparity amplitude was from 4 to 24 min arc. The results showed that pupillary responses can be elicited by all these stereo gratings except when either the spatial frequency or disparity amplitude was reduced to zero. When the disparity amplitude was fixed to 8 min arc, the pupillary response amplitude increased with increasing spatial frequency, eventually reaching a plateau. While the spatial frequency was fixed to 0.3 cpd, the pupillary response amplitude continued to increase within the range of disparity amplitude. This provides a different approach to demonstrate that these pupillary responses were induced by stereo information. In addition, the stereo pupillary responses may be further developed as an objective method to study stereopsis. Finally, plausible underlying mechanisms of the stereo pupillary response are discussed.

Depth Perception↗

PubMed2005

Diazepam-induced changes of optokinetic nystagmus fast phase.

Since specific benzodiazepine (Bz) binding sites have been found in the vision and oculomotor control areas of the central nervous system (CNS), the fast phases of optokinetic nystagmus (OKN) should be affected by Bz administration. In this study, we examine the effects of Bzs on OKN fast phases under closed- and open-loop experimental conditions. Six normal subjects participated in the experiments. The eye movements were measured by the magnetic field, search coil technique, 90 min after diazepam or placebo administration. The study was performed in a randomized, double-blind fashion. After diazepam, the mean amplitude (MAmp) and mean peak velocity (MVel) of OKN fast phases decreased significantly under both experimental conditions. The percentage decreases in MAmp and MVel under the open-loop condition were significantly larger than those under the closed-loop condition. The results indicate that the fast phases of OKN could sensitively reflect the pharmacodynamic effects of Bzs on the CNS.

Adult↗

PubMed2005

Effects of diazepam on the latency of saccades for luminance and binocular disparity defined stimuli.

Saccadic latency is composed of separate sensory and motor processing delays. Therefore, any alteration in the sensory processing should effect the saccadic latency. Because the highest density of benzodiazepine (Bz) binding sites is located in cerebral cortex, sensory processing of stimuli in this cortical area is expected to be substantially effected by administration of Bzs. It is well known that sensory processing of binocular disparity occurs in the cerebral cortical areas and therefore the latency of saccades to stimuli defined by binocular disparity should be substantially affected by Bz intake. In this study, we tested this prediction by comparing the latency of saccadic eye movements for binocular disparity defined stimuli (stereo stimuli) with those for luminance contrast defined stimuli (luminance stimuli), after diazepam or placebo. Eye movements were mainly recorded by use of the magnetic search coil technique, and the study was performed in a randomized, double-blind way. Although diazepam prolonged the latency of saccades for stereo and luminance stimuli, the percentage increases in saccadic latency for the stereo stimuli were significantly larger than those for the luminance stimuli. Saccadic peak velocity, and saccadic amplitude, also significantly decreased after diazepam under conditions of stereo and luminance stimuli. However, there was no significant difference for either saccadic peak velocity or amplitude between the two types of target. The results suggest that the latency of saccades to binocular disparity defined random-dot stimuli could more sensitively reflect the pharmacodynamic effects of Bzs on the cerebral cortex.

Adult↗

PubMed2004

Pupillary response induced by stereoscopic stimuli.

Besides luminance change, the pupil responds to changes in spatial pattern, color content and target motion. Our experimental results show that transient pupillary constriction can also be elicited by dichoptically viewing a change in stereoscopic stimuli composed of dynamic random-dot stereograms from an initially flat surface to a stationary sinusoidal grating shown in depth. On the other hand, monocular viewing of these stimuli produced no obvious pupillary response. This indicates that the pupillary response in the dichoptic experiment was induced by the stereo information rather than by any change in the monocular stimuli. This finding presents a novel approach for the investigation of stereo perception that can also be applied in the clinical environment.

Depth Perception↗

PubMed2003

Effects of diazepam on closed- and open-loop optokinetic nystagmus (OKN) in humans.

The effects of diazepam on optokinetic nystagmus (OKN) eye movements were studied under closed-loop and open-loop conditions in healthy humans. The open-loop condition was achieved by adding the eye-movement velocity signal of OKN to the computer-generated signal controlling the moving stimulus grating. Each of four subjects received a single oral dose of 5 mg diazepam or a placebo on two separate days in a double-blind randomized fashion. OKN eye movements were measured 90 min after administration of the treatments. As compared to placebo, diazepam significantly reduced the gain of open-loop OKN, but did not modify the gain of closed-loop OKN. The results indicate that the OKN gain under the open-loop condition is a more sensitive detector of the parameter changes of the OKN system than under the closed-loop condition. Thus, open-loop OKN gain can provide an objective, quantitative measure of benzodiazepine agonist effects.

Adult↗

PubMed2003

Alternating optokinetic nystagmus (OKN) induced by intermittent display of stationary gratings.

In this paper, we report a novel optokinetic nystagmus (OKN), which was evoked by stationary gratings presented intermittently. OKN eye movements were accurately measured by the electromagnetic scleral search-coil technique. For the luminance stimuli, alternating OKN was elicited when the interstimulus interval (ISI) ranged from 33 to 83 ms duration and the ISI luminance approximated to the mean luminance of the stimulus grating; for chromatic (red/green) stimuli, the OKN could be evoked in non-isoluminant condition and vanished in the isoluminant condition. It is a plausible explanation that the present OKN, intermittent display-of-gratings-induced OKN (IDG-OKN), might be related to the temporal impulse response of the luminance channel in vision.

Adult↗

PubMed2003

Interocular motion combination for dichoptic moving stimuli.

When gratings moving in different directions are presented separately to the two eyes, we typically perceive periods of the combination of motion in the two eyes as well as periods of one or the other monocular motions. To investigate whether such interocular motion combination is determined by the intersection-of-constraints (IOC) or vector average mechanism, we recorded both optokinetic nystagmus eye movements (OKN) and perception during dichoptic presentation of moving gratings and random-dot patterns with various differences of interocular motion direction. For moving gratings, OKN alternately tracks not only the direction of the two monocular motions but also the direction of their combined motion. The OKN in the combined motion direction is highly correlated with the perceived direction of combined motion; its velocity complies with the IOC rule rather than the vector average of the dichoptic motion stimuli. For moving random-dot patterns, both OKN and perceived motion alternate only between the directions of the two monocular motions. These results suggest that interocular motion combination in dichoptic gratings is determined by the IOC and depends on their form.

Adult↗

PubMed2002

Multi-directional shifts of optokinetic responses to binocular-rivalrous motion stimuli.

Previous dichoptic experiments showed that dissimilar stationary pattern stimuli resulted in the perception of binocular rivalry, whereas oppositely-directly moving grating stimuli resulted in alternating optokinetic nystagmus (OKN) and the perception of binocular motion rivalry. The present study extended these dichoptic motion experiments by introducing obliquely-oriented targets with the aim of probing further the cortical mechanisms underlying binocular processing of motion. Two-dimensional eye movements were recorded along with their subjective perceptual responses. The stimuli consisted of two tilted gratings, one moving diagonally upwards and to the right (UR, 45 degrees ) and the other diagonally upwards and to the left (UL, 135 degrees ), which were presented dichoptically to subjects under two stimulus modes. For the non-exchange mode, the OKN slow phases exhibited three types of directional shifts. Two of these directional shifts tracked the stimuli (i.e. UR or UL), whereas the third moved purely upwards (UP). Since physically there was no upward-moving target, the OKN and perceptual responses appeared to be associated with a perceptual interocular grouping of the two dichoptic stimuli in their reassembled vector-sum direction. The OKN shifts were also found to be highly correlated with the psychophysical responses of motion perception. For the rapid-exchange mode, in which the stimuli were rapidly exchanged between the two eyes, the OKN slow phases exhibited primarily two types of directional shifts, UR and UL, but no UP responses for most subjects. It also appeared that these two coherent motion percepts, UL and UR, were interocularly regrouped from the exchanged stimuli. Moreover, the lack of perceptual grouping to create an UP response in the rapid-exchange mode indicated that temporal integration of at least 200 ms was necessary for the development of a reassembled vector-sum-direction motion percept. The findings under both stimulus modes support the stimulus-feature rivalry hypothesis, in which higher cortical centers mediate interocular perceptual grouping and the associated motor response.

Cerebral Cortex↗

PubMed2002

Neostigmine-induced alterations in fast phase of optokinetic responses in myasthenic ocular palsies.

Closed-loop and open-loop optokinetic nystagmus (OKN) eye movements were recorded with an electromagnetic scleral search coil in 16 patients with myasthenic ocular palsies, 8 patients with nonmyasthenic ocular palsies, and 4 normal controls. We calculated the summation of fast-phase amplitude per second (SFPAps), mean of fast-phase amplitude (MFPA) and mean of fast-phase peak velocity (MFPV) of OKN before and after administration of neostigmine. Under open-loop conditions, the myasthenic patients group demonstrated distinct increases in three parameters: SFPAps (P < 0.000001), MFPA (P < 0.001) and MFPV (P < 0.001) following neostigmine injection, and the increase in SFPAps was greater than those of MFPA and MFPV (P < 0.02), while the other two groups showed no significant increases. Under closed-loop condition, only five of the myasthenic patients showed significant changes. These results suggest that the change in SFPAps during open-loop OKN before and after neostigmine administration was a specific measurement that differentiated patients with myasthenic ocular palsies from the other groups.

Adolescent↗

PubMed2002

Dual-directional optokinetic nystagmus elicited by the intermittent display of gratings in primary open-angle glaucoma and normal eyes.

PURPOSE: To compare optokinetic nystagmus (OKN) responses to the intermittent display of stimuli between normal subjects and patients with primary open-angle glaucoma (POAG). METHODS: Optokinetic nystagmus (OKN) was recorded in 9 glaucomatous patients and 7 normal subjects. The computer-generated stimuli displayed sinusoidal luminance gratings (16 cd/m(2) mean luminance, 0.5 cyc/deg) with a pi/2 phase shift between successive stimulus gratings. These stimulus gratings were separated by an interstimulus interval (ISI), during which a homogeneous luminance field of 16 cd/m(2) was presented. The ISI duration and the luminance contrast were set at different values. RESULTS: For normal subjects, dual-directional alternating OKN could be evoked in the ISI range from 33 to 100 ms. The dual-directional alternating OKN was defined as that OKN slow phase alternatively tracked in the direction of pi/2 shift (forward OKN) and against the pi/2 shift (reverse OKN). By contrast, for most glaucomatous eyes, nearly no reverse OKN could be evoked at any ISI value. CONCLUSIONS: The lack of reverse OKN in POAG patients in the present experiments is a meaningful finding. The occurrence of reverse OKN during a certain range of ISI duration could be related to the biphasic characteristics of the temporal impulse response in normal subjects, whereas, the lack of reverse OKN might suggest the plausible damage of magnocellular cells in POAG.

Adult↗